A “brake-by-wire” brake system for motor vehicles is known from DE 10 2010 040 097 A1 that has a brake pedal-operated tandem master brake cylinder, a simulator that is hydraulically connected to the master brake cylinder, an electrically controlled pressure supply device that is formed by a cylinder-piston assembly with a hydraulic pressure chamber, the piston of which can be displaced by an electromechanical actuator, and a pressure modulation unit for adjusting wheel-specific brake pressures comprising an inlet valve and an outlet valve per wheel brake. For performing normal braking in the “brake-by-wire” operating mode of the brake system, wheel brakes are subjected to the system pressure of the pressure supply device with the supply valves and inlet valves opened by the electrically controlled advancement of the piston of the pressure supply device. If the driver is carrying out panic braking, which causes entry into anti-lock control for all wheel brakes, the initial build-up of brake pressure at each of the wheel brakes on entry into anti-lock control must be terminated as quickly as possible. For this purpose, the inlet valves of all wheel brakes are closed and the advancement of the piston of the pressure supply device is terminated.
As high-pressure build-up gradients are initially wanted during panic braking for safety reasons, the pressure supply device or the driving electromechanical actuator thereof is operated highly or maximally dynamically in said situation. The closure of all inlet valves on entry into anti-lock control can then lead to a “post-displacement” of a volume of pressure medium from the pressure chamber of the pressure supply device, even in the case of a simultaneously output actuation command to stop the electromechanical actuator, owing to the inertia of the electromechanical actuator. This enables a very high back pressure to occur in the system, which can result in damage to the electromechanical actuator or in the extreme case to bursting of the system.
In DE 10 2011 077 329 A1, a method for controlling an electrohydraulic “brake-by-wire” brake system with an anti-lock control function, an inlet valve and an outlet valve per wheel brake and an electrically actuated pressure supply device is described, which comprises a cylinder-piston assembly with a hydraulic pressure chamber, the piston of which can be displaced by an electromechanical actuator. In this case, it is described in DE 10 2011 077 329 A1 that during anti-lock control at least one wheel brake is always connected, in the sense of complete pressure balance between the wheel brake and the pressure chamber, to the hydraulic pressure chamber of the pressure supply device via the associated open inlet valve, so that the brake pressure profile at said wheel brake is exclusively varied by the reciprocal movement of the piston of the pressure supply device. However, this is not reasonably possible in all braking situations.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.